It is known to produce plastic tamper evident caps for containers which employ telltale breakaway rings which indicate the condition of the containers, i.e., whether such containers have been opened or tampered with. Commonly, such caps are molded of plastic materials and include a skirt having a ring or band that extends downwardly therefrom and is in a generally cylindrical or conical relationship to the skirt, and which is attached thereto by a line or area of weakness, including posts, bridges and the like. Typically, the skirt also includes engaging means for engaging a container for closing and opening the container and the band includes interfering means which engage the container to prevent removal of the band upon initial removal of the cap, thereby causing the band to break or separate from the skirt at the line of weakness, leaving the band as a telltale condition of the container.
For example, it is known to form a peripheral bead around the inside portion of a breakaway band, which bead is adapted to engage the underside of a bead or shoulder projecting from the periphery of a container neck. Thereafter, when the cap is initially removed from a container, the bead engages the underside of the projecting bead in an interfering manner, and the force to separate the band at the line of weakness becomes less than the interference force, whereupon the breakaway band separates leaving a tamper evident ring on the container. Such a design is shown, for example, in U.S. Pat. No. 4,527,704.
In another example, it is also known to fold at a portion of reduced thickness the lower portion of a breakaway band inwardly and upwardly to produce a continuous band which generally has a "V" cross sectional shape adapted to engage the underside of the bead or shoulder on the container neck. Thereafter, when the described cap is initially removed from a container, the free end of the inverted continuous "V" shaped portion of the band engages the underside of the projecting bead in an interfering manner, whereupon the breakaway band separates at the line of weakness, leaving the tamper-indicating band on the container.
While conceptually serving a useful purpose, such cap designs, in practice, do not always function in a reliable manner. For example, the design which employs an interfering peripheral bead on the lower portion of a breakaway band is rigid and difficult to apply to a container neck, and it can disadvantageously produce significant levels of interference with the upper surfaces of the container neck including the projecting bead upon capping. Such capping interference may require an undesirable excess of force to secure the cap on the container, possibly leading to the premature rupture of the line of weakness during the capping operation, or in cap misalignment and/or permanent deformation to structural features of the cap or container, or distortion of engaging beads, all of which may result in such a cap not being fully applied to the container neck or other nonsatisfactory performance. Further, once snapped in place, an interfering bead by virtue of a rounded configuration, only provides a limited surface for engagement, for example, with the outside peripheral horizontal underside surface of a container neck projecting bead. Such an engagement may be separated by relatively little force enabling the breakaway band and the entire cap to be removed intentionally from the container neck without rupturing the line of weakness, thereby defeating the purpose of the tamper indicating features.
The design which employs a continuous "V" shaped portion on the lower end of a breakaway band offers improvement over the peripheral bead design in providing significant levels of interference, for example, with the underside of an interfering container bead upon initial cap removal, thereby insuring the rupture of the line of weakness and that the breakaway portion remains on the container neck. Such breakaway band portions, however, also disadvantageously produce significant levels of interference with the upper surface of the container neck finish and projecting bead upon capping leading to problems such as discussed above.
Attempts to solve these problems have included the formation of a cap with a lower breakaway ring having interfering means which include upwardly and inwardly folded independent tabs which lock against a projecting bead or annular shoulder on a container neck to retain the tamper-indicating breakaway ring on the neck when the cap is initially removed from the container. Tabs of this type of tamper-indicating means are independent of one another and are connected at their folds to the bands of the cap. An example of such a design is described in U.S. Pat. No. 4,506,795. While this design facilitates ease of cap application and alignment, such independent interfering tabs, however, can quite easily be manipulated to maneuver the folded tabs over the projecting bead on a container neck to remove the breakaway ring portion and the entire cap, thus defeating the purpose of the tamper-indicating feature.
Other existing considerations and problems relate to the production of tamper evident caps. For example, it is desirable that the circumferentially continuous band portions of a breakaway ring be made thin so that they are easily removed from a mold after their fabrication, and are sufficiently flexible to permit the easy application of a cap to a container neck. On the other hand, it is desirable to employ a breakaway band of strength and rigidity to inhibit manipulation while providing the requisite interference upon initial removal of the cap.
The previously described caps, including a band with a molded solid bead or the like, do not meet these objectives. The bead increases the axial force needed to axially strip the cap from the mold, thereby subjecting the bridges, posts or the like to axial forces which could cause premature fracturing, even before the cap is removed from the mold.
While existing caps, which include post forming techniques, may overcome mold stripping problems, these caps are beset by a number of other problems. As already described, the problems include difficulties in capping or in ease of undesirable manipulation of the caps.
Also, the means which provide the line of weakness between the skirt of the cap and the breakaway or separable band must be capable of being stripped from the mold. For example, presently available caps provide fracturable bridges or posts between the cap skirt and band at angles which, typically, are vertical or in some case at an angle of up to about 45.degree. from the vertical. As an angle from the vertical the bridges can offer significant interference to removal from a mold by stripping and, because of their intended fragile nature, they are therefore typically produced in side acting movable mold sections so that the cap may be removed from the mold intact including its bridges and depending band. Such separately acting mold sections are more susceptible to wear which can affect the sharpness of the notch created by the bridge and the bottom of the skirt, thereby reducing notch sensitivity and tamper evident performance of the cap. U.S. Pat. Nos. 4,573,601 and 4,505,401 are illustrative of patents which describe frangible bridges which are at about 45.degree. to the horizontal. At such angles, however, substantial axial forces and longer cap and container engagement may be required to fracture the bridges upon initial removal of the cap especially as tool wear affects the notch sensitivity at the bridge attachment sites. As a consequence, additional height and thread length may be needed for the cap and container, resulting in increased costs in material and manufacture. The approximately 45.degree. angle may not provide sufficient "notch sensitivity," i.e. minimial axial forces at the attachment sites to the cap skirt and breakaway band for readily breaking the bridges upon initial removal of the cap from the container. In addition, bridges, posts and the like commonly are made relatively thin in an attempt to minimize the axial forces needed for fracturing upon initial removal of the cap. However, in manufacture, packaging, handling and capping the caps are subjected to radial forces which can prematurely fracture the thin bridges or posts, rendering the cap useless for their intended purpose.
Thus, there is a need for tamper evident caps and methods of forming the caps which overcome deficiencies in existing caps and methods.